The sooner you start thinking of guns in simple forms, the better. Guns are actually ridiculously easy once you have
a) good reference
b) good handling on perspective
c) good idea of how those guns break down into simple shapes
If it helps, a way to think about it is sculpting. A classic revolver is composed of maybe three, four various sized rectangles (barrel, cylinders, handle, and maybe hammer, if it's pronounced enough.)
It's kinda like life-drawing, honestly, which is funny. If you pay attention to the proportions of the gun (which REALLY affect how believable it looks) and what simple shapes it's composed of, you can start drawing them really well.
A good book for reference is The Illustrated Book of Guns, by Edward Miller. I dunno how hard it is to find (found it in the bargain bin at a Barnes and Noble,) but it has a lot of photos of different guns, most if not all of them sideviews and all that.